1) Field of the Invention
This invention relates to a wavelength multiplexing transmission apparatus and a wavelength demultiplexing reception apparatus suitable for use with wavelength multiplex transmission of a high density.
2) Description of the Related Art
In recent years, a demand for increase in capacity of a transmission apparatus has been and is progressively increasing as the information society advances progressively. Particularly, increase of the speed in electronics (an increase in transmission speed of an electric signal) is getting difficult after the speed exceeds 10 Gb/s, and it is anticipated significantly to achieve an increase in capacity by an increase. in speed on an optical signal level, particularly, by signal transmission to which a wavelength multiplex system is applied.
As a wavelength multiplex system, narrow-band wavelength multiplexing in the 1.55 xcexcm band which provides a wavelength with which the loss of an optical fiber is lowest is considered promising and has already been put into practical use. Further, since this wavelength band coincides with an application wavelength band of an optical amplifier for which an optical fiber doped with erbium is used and also the loss of a wave combiner/separator provided for performing wavelength multiplexing or wavelength demultiplexing can be compensated for by the optical amplifier, wavelength multiplexing of such a large number of waves that is not conventionally available can be performed.
However, in a transmission apparatus which adopts such a wavelength multiplex system as described above, when wavelength arrangement of the wavelengths of a plurality of transmission optical signals (transmission lights) is performed in a narrow band and in a high density in the 1.55 xcexcm band, small variations occur with the wavelengths of the transmission light signals by various causes, and also where a small wavelength variation occurs with some transmission light in this manner, the signal of the channel may not be transmitted successfully or may have an influence on the optical signal of a wavelength of an adjacent channel and bring about crosstalk with the adjacent channel.
In such an instance, a communication error may possibly occur not only with the channel with which the wavelength variation occurs but also with the channel with which the crosstalk occurs.
Accordingly, a transmission apparatus which performs high density wavelength multiplexing or wavelength demultiplexing described above not only has a subject to be solved in that wavelengths of transmission light sources must be stabilized, but also has another subject in that, should wavelength displacement occur, crosstalk with another channel must be prevented.
Further, while some optical signal transmission apparatus include a temperature stabilization circuit or a like circuit for a light source in order to secure stability of the temperature, where the stability of a thermistor which monitors the environment temperature of the light source is not sufficiently high, there is a subject in that it must be taken into consideration that a variation may occur because of deterioration of the thermistor as time passes. On the other hand, also there is another subject in that care must be taken of deterioration of a transmission light source itself which outputs an optical wavelength as time passes.
It is an object of the present invention to provide a wavelength multiplexing transmission apparatus and a wavelength demultiplexing reception apparatus wherein a variation of a wavelength of a transmission light source is detected to prevent that such variation causes crosstalk with another channel.
In order to attain the object described above, according to an aspect of the present invention, there is provided a wavelength multiplexing transmission apparatus, comprising a plurality of optical signal outputting sections for outputting optical signals having different wavelengths from each other, and a wavelength multiplexing section for wavelength multiplexing the optical signals outputted from the optical signal outputting sections and sending out a resulting optical signal, each of the optical signal outputting sections including a transmission light source and a wavelength filter.
The transmission light source is driven by an electric signal for outputting an optical signal of a predetermined wavelength, and the wavelength filter is capable of passing therethrough and sending out only an optical signal of the predetermined wavelength to be outputted from the transmission light source to prevent a wavelength drift of the optical signal outputted from the transmission light source.
Accordingly, with the wavelength multiplexing transmission apparatus, since, in each of the optical signal outputting sections, the transmission light source is driven by an electric signal to output an optical signal of the predetermined wavelength and the wavelength filter can pass therethrough and send out only the predetermined wavelength to be outputted from the transmission light source to prevent a wavelength drift of the optical signal outputted from the transmission light source, any optical wavelength displaced out of a pertaining predetermined normal range is attenuated by the pertaining wavelength filter and is not transmitted as a wavelength multiplex signal. Consequently, the wavelength multiplex transmission apparatus is advantageous in that crosstalk with another channel can be prevented.
The wavelength multiplexing transmission apparatus may be constructed such that each of the optical signal outputting sections further includes a first abnormal condition detecting section for supervising a level of the optical signal sent out from the wavelength filter and detecting an abnormal condition when the level is lower than a first threshold level set in advance.
The wavelength multiplexing transmission apparatus having the construction just described is advantageous in that, since the first abnormal condition detecting section in each of the optical signal outputting sections supervises a level of the optical signal sent out from the wavelength filter, by discriminating whether or not the level of the optical signal is lower than the first threshold level set in advance, an abnormal condition of the light source wavelength can be detected.
The wavelength multiplexing transmission apparatus may be constructed such that each of the optical signal outputting sections further includes a second abnormal condition detecting section for detecting an abnormal condition of an output level of the optical signal outputted from the transmission light source, and a third abnormal condition detecting section for detecting an abnormal condition of a wavelength of the optical signal outputted from the transmission light source when an abnormal condition is detected by the first abnormal condition detecting section and a normal condition is detected by the second abnormal condition detecting section.
The wavelength multiplexing transmission apparatus having the construction just described is advantageous in that, since, in each of the optical signal outputting sections, the second abnormal condition detecting section detects an abnormal condition of an output level of the optical signal outputted from the transmission light source and the third abnormal condition detecting section supervises results of detection of the first abnormal condition detecting section and the second abnormal condition detecting section, not only an abnormal condition of the light source but also a wavelength displacement can be detected.
According to another aspect of the present invention, there is provided a wavelength multiplexing transmission apparatus, comprising a plurality of optical signal outputting sections for outputting optical signals having wavelengths different from each other, and a wavelength multiplexing section for wavelength multiplexing the optical signals outputted from the optical signal outputting sections and sending out a resulting optical signal, each of the optical signal outputting sections including a light source module, a temperature control section, an ambient temperature detecting section and a fourth abnormal condition detecting section.
The light source module includes a transmission light source, a temperature detecting section, and a heating/cooling section. The temperature detecting section detects an environment temperature of the transmission light source, and the heating/cooling section varies the environment temperature of the transmission light source.
The temperature control section outputs a control signal based on the temperature information detected by the temperature detecting section to the heating/cooling section to control the heating/cooling section so that the environment temperature may be stabilized at a reference temperature set in advance. The fourth abnormal condition detecting section detects an abnormal condition of the light source module based on the control signal from the temperature control section to the heating/cooling section and ambient temperature information detected by an ambient temperature detecting section provided for detecting an ambient temperature of the light source module.
The wavelength multiplexing transmission apparatus of the construction just described is advantageous in that, since, in each of the optical signal outputting sections, the temperature control section outputs a control signal based on the temperature information detected by the temperature detecting section to the heating/cooling section of the light source module, which includes the transmission light source, the temperature detecting section and the heating/cooling section, to control the heating/cooling section so that the environment temperature may be stabilized at the reference temperature set in advance and the fourth abnormal condition detecting section supervises the control signal from the temperature control section to the heating/cooling section and ambient temperature information detected by the ambient temperature detecting section, a wavelength abnormal condition can be detected indirectly by detecting an abnormal condition of a temperature stabilization circuit for the light source which is provided for wavelength stabilization.
According to a further aspect of the present invention, there is provided a wavelength multiplexing transmission apparatus, comprising a plurality of optical signal outputting sections for outputting optical signals having wavelengths different from each other, and a wavelength multiplexing section for wavelength multiplexing the optical signals outputted from the optical signal outputting sections and sending out a resulting optical signal, each of the optical signal outputting sections including a transmission light source driven by an electric signal for outputting an optical signal of a predetermined wavelength, a driving signal control section for controlling the electric signal for driving the transmission light source so that a level of the electric signal for driving the transmission light source may be stabilized at a reference level, and a fifth abnormal condition detecting section for detecting an abnormal condition of the transmission light source based on the level of the electric signal for driving the transmission light source which is controlled by the driving signal control section.
With the wavelength multiplexing transmission apparatus, since, in each of the optical signal outputting sections, the driving signal control section controls the electric signal for driving the transmission light source so that the level of the electric signal for driving the transmission light source may be stabilized at the reference level and the fifth abnormal condition detecting section supervises the level of the electric signal for driving the transmission light source which is controlled by the driving signal control section, there is an advantage that an abnormal condition of the driving current of the transmission light source can be detected and an abnormal condition of the wavelength of the transmission light source can be detected.
According to a still further aspect of the present invention, there is provided a wavelength multiplexing transmission apparatus, comprising a plurality of optical signal outputting sections for outputting optical signals having wavelengths different from each other, and a wavelength multiplexing section for wavelength multiplexing the optical signals outputted from the optical signal outputting sections and sending out a resulting optical signal, each of the optical signal outputting sections including a light source module including a transmission light source for outputting an optical signal of a predetermined wavelength, a temperature detecting section for detecting an environment temperature of the transmission light source, and a heating/cooling section for varying the environment temperature of the transmission light source, a temperature control section for outputting a control signal based on the temperature information detected by the temperature detecting section to the heating/cooling section to control the heating/cooling section so that the environment temperature may be stabilized at a reference temperature set in advance, an ambient temperature detecting section for detecting an ambient temperature of the light source module, a fourth abnormal condition detecting section for detecting an abnormal condition of the light source module based on a relationship between the control signal from the temperature control section to the heating/cooling section and the ambient temperature information detected by the ambient temperature detecting section, a driving signal control section for controlling an electric signal for driving the transmission light source so that a level of the electric signal for driving the transmission light source may be stabilized at a reference level, a fifth abnormal condition detecting section for detecting an abnormal condition of the light source module based on the level of the electric signal for driving the transmission light source which is controlled by the driving signal control section, and a sixth abnormal condition detecting section for detecting an abnormal condition of a wavelength of the optical signal outputted from the transmission light source when an abnormal condition is detected by the fourth abnormal condition detecting section or the fifth abnormal condition detecting section.
With the wavelength multiplexing transmission apparatus, since, in each of the optical signal outputting sections, the fourth abnormal condition detecting section supervises the control signal from the temperature control section to the heating/cooling section and the ambient temperature detected by the ambient temperature detecting section while the fifth abnormal condition detecting section supervises the level of the electric signal for driving the transmission light source which is controlled by the driving signal control section and the sixth abnormal condition detecting section supervises results of detection of the fourth abnormal condition detecting section and the fifth abnormal condition detecting section, there is an advantage that a wavelength abnormal condition can be detected indirectly by detecting an abnormal condition of a temperature stabilization circuit for the light source which is provided for wavelength stabilization, and also there is another advantage that an abnormal condition of the driving current for the transmission light source can be detected and an abnormal condition of the wavelength of the transmission light source can be detected.
The wavelength multiplexing transmission apparatus may be constructed such that, when an abnormal condition of the light source module or the transmission light source is detected, the optical signal to be outputted from the optical signal outputting section to the wavelength multiplexing section is switched into an interruption condition.
With the wavelength multiplexing transmission apparatus having the construction just described, there is an advantage that, when an abnormal condition of the light source module or the transmission light source is detected, by switching the optical signal to be outputted from the optical signal outputting section, with which the abnormal condition is detected, to the wavelength multiplexing section into an interruption condition, crosstalk with another channel can be prevented and a further influence of it can be prevented.
According to a yet further aspect of the present invention, there is provided a wavelength demultiplexing reception apparatus, comprising a wavelength demultiplexing section, a plurality of light reception sections, a plurality of error detecting sections, and a first transmission side wavelength abnormal condition detecting section.
The wavelength demultiplexing section receives, from a transmission side, a wavelength multiplexed optical signal including data having a predetermined format and demultiplexes the optical signal into a plurality of optical signals having wavelengths different from each other and same as those prior to the wavelength multiplexing.
Each of the light reception sections includes an interruption condition detecting section, which converts a pertaining one of the optical signals demultiplexed by the wavelength demultiplexing section into an electric signal and outputs, when the optical signal inputted to the light reception section is put into an interruption condition, detection information representing the interruption.
The error detecting section detects a data error with respect to the predetermined format from data included in the electric signals after the conversion by the light reception sections.
The first transmission side wavelength abnormal condition detecting section detects a wavelength with which an abnormal condition occurs from among wavelengths of the optical signals for which the wavelength multiplexing has been performed on the transmission side based on the detection information of the interruption condition detecting sections of the light reception sections and the data error detection information from the error detecting sections.
With the wavelength multiplexing transmission apparatus, there is an advantage that, since the wavelength demultiplexing section demultiplexes a wavelength multiplexed optical signal received from the transmission side and including data having a predetermined format into a plurality of optical signals having wavelengths different from each other and same as those prior to the wavelength multiplexing and the interruption condition detecting section of each of the light reception sections receives and converts a pertaining one of the optical signals demultiplexed by the wavelength demultiplexing section into an electric signal and outputs, when the optical signal inputted to the light reception section is put into an interruption condition, detection information representing the interruption and besides the error detecting sections detect a data error with respect to the predetermined format from data included in the electric signals after the conversion by the light reception sections and the first transmission side wavelength abnormal condition detecting section supervises the detection information of the interruption condition detecting sections of the light reception sections and the data error detection information from the error detecting sections, there is an advantage that an abnormal condition of the wavelength can be detected. Further, should some wavelength displacement of a signal light source of any of the wavelength multiplexing transmission apparatus occur, since the light source with which the wavelength displacement occurs can be specified, there is an another advantage that a countermeasure of replacement of a panel and/or release from the trouble can be taken rapidly.
The wavelength demultiplexing reception apparatus may be constructed such that the first transmission side wavelength abnormal condition detecting section is operable to detect that an abnormal condition occurs with a wavelength of one of two optical signals having adjacent wavelength bands to each other from among the optical signals for which the wavelength multiplexing has been performed on the transmission side when an interruption condition of one of the two optical signals which has a first wavelength is detected by a corresponding one of the interruption condition detecting sections and a data error of the optical signal which has a second wavelength is detected by a corresponding one of the error detecting sections.
The wavelength demultiplexing reception apparatus having the construction just described is advantageous in that, since the first transmission side wavelength abnormal condition detecting section supervises each two adjacent optical signals, an optical signal outputting section with which a wavelength abnormal condition occurs can be specified.
The wavelength demultiplexing reception apparatus may further comprise a transfer section for transferring, when it is detected by the first transmission side wavelength abnormal condition detecting section that an abnormal condition occurs with a wavelength of one of two optical signals, abnormal condition detection information representing such detection to the transmission side so that the optical signal of the wavelength with which the abnormal condition occurs may be put into an interruption condition.
The wavelength demultiplexing reception apparatus having the construction just described is advantageous in that, as the transfer section transfers abnormal condition detection information for putting the optical signal of the wavelength with which the abnormal condition occurs into an interruption condition, crosstalk with another channel can be prevented and a further influence of it can be prevented.
The wavelength demultiplexing reception apparatus may be constructed such that the transfer section uses one of ascending and descending lines between the wavelength demultiplexing reception apparatus and the transmission side which is different from that line which is used for transmission of the wavelength multiplexed optical signal from the transmission side.
With the wavelength demultiplexing reception apparatus having the construction just described, there is an advantage that, since, when the transfer section tries to transfer abnormal condition detection information to the transmission side, it uses one of the lines which is different from that one of the lines which is used for transmission of the wavelength multiplexed optical signal from the transmission side, an optical wavelength which may possibly cause crosstalk with another channel can be interrupted.
According to a yet further aspect of the present invention, there is provided a wavelength demultiplexing reception apparatus, comprising a branching section, a plurality of variable wavelength filters, a plurality of filter control sections and a second transmission side wavelength abnormal condition detecting section.
The branching section receives a wavelength multiplexed optical signal from a transmission side and power branches the received wavelength multiplexed optical signal into a number of wavelength multiplexed optical signals equal to a number of multiplexed wavelengths different from each other.
The variable wavelength filters receive the wavelength multiplexed optical signals power branched by the branching section and pass optical signals of the different wavelengths therethrough.
The filter control sections output control signals to the variable wavelength filters to control the wavelengths of optical signals which can pass through the variable wavelength filters to follow up and pass the optical signals outputted from the variable wavelength filters, respectively.
The second transmission side wavelength abnormal condition detecting section detects, based on the control signals outputted from the filter control sections, a wavelength with which an abnormal condition occurs from among the wavelengths of optical signals for which the wavelength multiplexing has been performed on the transmission side.
With the wavelength demultiplexing reception apparatus, there is an advantage that, since the branching section power branches a wavelength multiplexed optical signal received from the transmission side into a number of wavelength multiplexed optical signals equal to the number of multiplexed wavelengths and the variable wavelength filters pass therethrough the optical signals of the wavelengths different from each other and same as those prior to the wavelength multiplexing from among the wavelength multiplexed optical signals power branched by the branching section and then the filter control sections output control signals to the variable wavelength filters so as to follow up and pass the optical signals outputted from the variable wavelength filters and the second transmission side wavelength abnormal condition detecting section supervises the control signals outputted from the filter control sections, a wavelength abnormal condition can be detected.
The wavelength demultiplexing reception apparatus may further comprise a transfer section for transferring, when it is detected by the second transmission side wavelength abnormal condition detecting section that an abnormal condition occurs with the wavelength of one of the optical signals, abnormal condition detection information representing the abnormal condition to the transmission side in order to put the optical signal of the wavelength with which the abnormal condition occurs into an interruption condition.
With the wavelength demultiplexing reception apparatus having the construction just described, there is an advantage that, as the transfer section transfers abnormal condition detection information for putting the optical signal of the wavelength with which the abnormal condition occurs into an interruption condition to the transmission side, crosstalk with another channel can be prevented and a further influence of it can be prevented.
The wavelength demultiplexing reception apparatus may be constructed such that the transfer section uses one of ascending and descending lines between the wavelength demultiplexing reception apparatus and the transmission side which is different from that line which is used for transmission of the wavelength multiplexed optical signal from the transmission side.
With the wavelength demultiplexing reception apparatus having the construction just described, there is an advantage that, since, when the transfer section tries to transfer abnormal condition detection information to the transmission side, it uses one of the lines which is different from that one of the lines which is used for transmission of the wavelength multiplexed optical signal from the transmission side, an optical wavelength which may possibly cause crosstalk with another channel can be interrupted with certainty.